1. Field of the Invention
The present invention relates to an improvement of a Hall element in respect of heat dissipation and noise characteristic without deteriorating the bias current versus Hall voltage characteristic.
2. Description of the Prior Art
The formula for expressing the fundamental characteristic of a Hall element having a substantially criss-cross geometrical configuration includes a Hall coefficient which provides a constraint to the material to be used for the Hall element. In general, use of a high purity semiconductor material is most preferred. Because such material exhibits a relatively high resistance, generation of Joule heat is necessarily involved due to the voltage drop corresponding to a product of the resistance of the Hall element and the bias current I.sub.H thereof. Thus, when the Hall element is operated under relatively severe conditions, temperature rise of the Hall element ascribable to the Joule heat thereof will result in a reduction of the Hall coefficient R.sub.H and hence, a correspondingly reduced Hall voltage V.sub.H.
In the measurement of a weak magnetic field or magnetic flux in a small area in which the use of Hall element is increasingly demanded, it is necessary to decrease the length l of a magneto-sensitive portion of the Hall element 2 of a substantially criss-cross configuration such as shown in FIG. 1 and hence to decrease correspondingly the width w of the magneto-sensitive portion, which results in the corresponding decrease in the detected magnetic flux .phi.. In this connection, the term "magnetosensitive portions" is intended to mean a rectangular portion of a Hall element which serves positively for generation of a Hall voltage in response to magnetic flux of a magnetic field to be detected or measured. In an effort to enhance the sensitivity of the Hall element, it has been hitherto known that the bias current I.sub.H is increased to thereby increase the output voltage or a ferromagnetic material having a low magnetic reluctance is employed with the magnetic flux being concentrated on the magneto-sensitive portion whereby the density of magnetic flux in appearance in the magneto-sensitive portion is increased to attain a high Hall voltage or a high output voltage. However, miniaturization of the magneto-sensitive portion as well as the increased bias current I.sub.H in turn incur degradation in the heat dissipation property for Joule heat generated in the Hall element, necessarily giving rise to a temperature rise in the Hall element which tends to lower the Hall voltage. In view of the circumstances, there is a need for a more effective heat dissipation technique to enhance the Hall voltage V.sub.H.
As an approach to solve the above problem, the Japanese Utility Model Application Kokai (Laid-Open) No. 49-107962 discloses a particular geometrical configuration of a Hall element directed to an improved heat dissipation efficiency, which is herein cited for reference. FIG. 1 illustrates dimensional relationship defining the geometrical configuration of a Hall element according to the prior proposal. Referring to this figure, input terminal electrodes 5 and 5' for supplying a bias current are provided at both ends of a slab (main body) 2 of a Hall element by depositing electrically conductive metal in the form of a laminated layer. A pair of contiguous projection 6 and 6' are integrally formed at both lateral sides of the slab 2 in opposition to each other. The projecting arms 6 and 6' are formed with output terminal electrodes 4 and 4' for detecting a Hall voltage, respectively, by depositing an electrically conductive metal layer onto the exposed end faces thereof. In such a Hall element, the proper proposal teaches that the heat generation in the Hall element can be suppressed at minimum when the following dimensional relationships are realized: ##EQU1## where w: the width of the slab 2,
s: the width of the integral arm 6, 6', PA1 l.sub.1 : the projecting length of the arm 6, 6' and PA1 l.sub.2 : the distance between a lateral edge of the arm (6, 6') and the adjacent input terminal electrode (5, 5'). PA1 l=length of the magneto-sensitive portion in the direction along the bias current flow, PA1 w=width of the magneto-sensitive portion in the direction perpendicular to that of the bias current, PA1 s=width of the second regions over which each of the second regions is contiguous to the magneto-sensitive portion, PA1 .theta.=angle formed between a lateral edge of the magneto-sensitive portion and a peripheral edge of an enlarged region provided contiguously to the magento-sensitive portion at both ends thereof, PA1 L=overall length of the Hall element in the direction of the bias current minus lengths of the input electrodes, and PA1 W=width of the enlarged region in the direction perpendicular to the bias current flow.
However, the attempt to suppress the heat generation in connection with an increased output voltage (i.e., Hall voltage) of the Hall element is not the positive measure. Even the Hall element realized with the above dimensional requirements fulfilled has proven to be still unsatisfactory for obtaining a desired high Hall voltage, as described hereinafter. Besides, it has been found that noise characteristics of the Hall element attributable more or less to the geometrical configuration thereof which are mentioned and considered neither in the above-referenced prior art nor any other literatures must be improved.